Method and device for detecting contaminants in a fluid

ABSTRACT

The invention relates to a method and a device for detecting contaminants in a fluid ( 1 ), wherein the fluid ( 2 ) that is contaminated with particles is conveyed by a first metering pump ( 3 ) to a device ( 4 ) for measuring the contamination or the particle density in the contaminated fluid ( 2 ). Said method and said device are each characterized in that, before entering the device ( 4 ) for measuring the contamination, the fluid is mixed with purified fluid ( 5 ) in a defined mixing ratio, the particle density or the contamination of the mixed fluid ( 6 ) is measured, and the particle density or the contamination of the contaminated fluid ( 2 ) is determined by an arithmetic unit ( 7 ).

The invention relates to a method for detecting contaminants in a fluid according to the preamble of claim 1 and a device for carrying out the method according to claim 4.

Fluids, especially lubricating oils or the like, are exposed to a continuous ingress of contaminants in the form of ferromagnetic particles or other metallic particles or other particles of contaminants in the operation of systems or devices. Here a certain maximum concentration of contaminants, depending on the application, can be tolerated for the operation of a system or of devices. Especially for rolling oils, as are used in the steel industry or heavy industry, under certain circumstances large amounts of contaminants are introduced; their content can hardly be determined with sensors according to the prior art.

Such a device is described, for example, in EP 290 397 B1. A sensor for detecting the content of ferromagnetic particles in a fluid has a primary magnetic circuit which is formed by a permanent magnet. The primary magnetic circuit has an air gap which can be exposed to the fluid in order to cause the particles to collect in the vicinity of the air gap. The sensor furthermore has a Hall element which detects the change of the magnetic flux depending on the collected contaminants. A proportional detector signal is achieved on the content of particles of contaminants in the fluid. A secondary magnetic circuit with an induction coil is designed to counteract the primary magnetic circuit of the permanent magnet up to a complete extinction of the magnetic field in the air gap. In this way, detachment of the particles which have collected in the air gap is enabled. The known sensors and measuring methods for determining the contamination of a fluid are, however, inherently unsuited to a substantial ingress of contaminants or ingress of metallic particles.

Therefore, the object of the invention is to specify a device and a method for operating the device with which very high concentrations of contaminants in a fluid can be determined.

This object is achieved with a method according to claim 1 and with a device according to claim 4.

In that a contaminated fluid, before it is routed to a sensor or a device for measuring the contamination, is diluted by adding a defined amount of cleaned, particle-free and contaminant-free fluid to such an extent that the particle density can be measured with the device, the degree of contamination in a fluid can be determined with known measuring methods. Then the particle density or the degree of contamination of the undiluted fluid is computed by a control and/or regulation means or an arithmetic unit. The basic structure of the two fluids is preferably the same.

In a first exemplary embodiment, the contaminated fluid and the cleaned fluid are mixed with one another in a mixing means which can be represented both by a tank and also by a mixing valve.

In a device for carrying out the method, there is a metering circuit, that is, a hydraulic system, with which the contaminated fluid is routed to the device for measuring the contaminants by means of a first pump or metering pump.

The metering pump which is designed for transport of raw contaminated fluid, such as, for example, rolling oil, viewed in the fluid direction, is located upstream of a first valve V₁, which is designed preferably as a 3/2 directional control valve. Depending on the operating position of this first valve V₁, contaminated fluid can travel either into the metering circuit to the tank or can be relayed in the direction of a connecting site of the main hydraulic system.

Furthermore, the device has a primary circuit which comprises a second metering pump which delivers contaminated and/or cleaned fluid to a sensor. A third valve V₃ and a fourth valve V₄ are designed to implement a cleaning mode or a mixing mode for cleaned and contaminated fluid together with the valves of the metering circuit. Furthermore, a measuring mode or an evacuation mode for the two circuits can be represented therewith.

A functional combination of metering circuit and primary circuit can be effected by the control and/or regulation means such that the metering circuit remains in a preparation mode or standby mode and the primary circuit is transferred into a cleaning mode for removing the contamination upstream of the sensor.

The indicated method according to the invention for detecting contaminants in a fluid can be operated preferably in the following operating modes. To clean the oil, which is located in the tank, it is provided that the first valve V₁ is in its enabled position so that highly contaminated fluid in the form of the rolling oil is conveyed through, by means of the first metering pump, in the direction of the connecting site to the main hydraulic system, wherein the first metering pump per unit of time continues to convey a large amount of fluid so that lines in the main hydraulic system can be flushed and deposits can be prevented. The rolling oil, within the scope of its current contamination, is thus conveyed back into the main hydraulic system.

The primary circuit, which has been decoupled for this purpose from the metering circuit relative to the valve V₂, has an enabling operating position so that the measuring device is bypassed. The valves V₃ and V₄ are switched such that in the closed circuit, fluid from the tank is conveyed through a filter adjoining the valve V₄ and is returned cleaned to the tank. In this way, the delivery rate of the other metering pump per unit of time is also high.

In the “measuring” operating mode, for purposes of checking the cleanliness of the mixed oil stored in the tank, the metering circuit, as described above, is decoupled again from the primary circuit, and the valve V₂, as a bypass valve, is kept in its blocked position in order in this way to route the fluid through the measuring device. Furthermore, the valve V₄ is switched such that the cleaning filter is bypassed. In this measuring operation, the delivery rate of the second metering pump of the primary circuit is chosen to be small.

In the “mixing” and “metering” operating mode, the metering circuit which leads to the mixing tank is in operation, i.e., the valve V₁ is switched such that contaminated fluid of the main hydraulic system travels into the tank.

The metered addition takes place either via a cycling of the valve V₁ or by corresponding reduction of the fluid delivery amount per unit of time through the first metering pump. The other metering pump of the primary circuit in turn has a high fluid delivery amount per unit of time; and the measuring device in the form of the contamination sensor CS is again bypassed via the switched valve V₂. The valves V₃ and V₄ are switched such that the filter is again bypassed, and in this way fluid is returned directly from the valve V₄ into the tank.

This operating position relative to the primary circuit also corresponds to the “mixing” of the fluid in the primary circuit, the metering circuit then being decoupled from the tank by switching of the valve V₁ and in turn contaminated fluid continuing to be delivered into the main hydraulic system with a high fluid delivery rate by the first metering pump. The latter operating position, with the metering pump decoupled from the primary circuit, also corresponds to the actual measuring process, that is, the measuring analysis to be carried out, in which, however, the valve V₂ is blocked so that fluid is routed through the measuring device in the form of the contamination sensor by means of the other metering pump at low fluid delivery rate.

When a desired liquid level in the tank is exceeded, the device can be operated in an evacuation process in which tank fluid travels directly via the switched valve V₂ into the connection to the main hydraulic system, bypassing the measuring device by means of enabled valve V₃, the valve V₄ then being in its blocked position. This evacuation can take place until the desired liquid level in the tank, which can correspond to a minimum liquid level in the tank, is in turn reached.

In another embodiment, the sensor element is a Hall element which is mounted at a collecting site which is intended for the quantity of contaminants, especially in the form of ferromagnetic particles. The sensor element determines the quantity of contaminants in the mixed fluid and transmits the output signal to a control means and/or regulation means. It can be advantageous to store a table of values in the control means and/or regulation means, which table establishes a relationship between the degree of dilution of the quantity of the contaminant and the output signal of the sensor element which may also be highly nonlinear in this respect. The table of values can be based on empirically determined values. Alternatively, in the control means and/or regulation means, a function which has been determined, for example, by simulation can also be stored; said function represents the relationship between the amount of collected contaminant and the output signal of the sensor, depending on the degree of dilution of the fluid.

Depending on the measured values, the control means and/or the regulation means controls the metering circuit and the primary circuit in the combination of the above-described operating modes. In this connection, it can be advantageous, especially when metallic/ferrometallic particles or contaminants are to be detected, in the device for measuring the contaminants for there to be a collecting site for collecting the contaminant of the fluid, in the form of a permanent magnet. The latter is used to generate a magnetic field at the collecting site. A coil can be provided to move an element in the manner of an armature such that by moving the element, the magnetic field strength at the collecting site can be changed, especially can be reduced to such a degree that at least one part of the collected contaminant can be detached from the collecting site, in particular can be flushed out of the fluid of the metering circuit.

Other advantages, features, and details of the invention will become apparent from the dependent claims and the following description in which an exemplary embodiment of the invention is detailed with reference to the drawings.

The figures are schematic and not to scale.

FIG. 1 is a hydraulic diagram in the manner of a function diagram relating to a device for carrying out a method for detecting contaminants;

FIG. 2 is a flow chart of a method for detecting contaminants in a fluid by means of a device as shown in FIG. 1;

FIGS. 3 to 5 show different function diagrams of the device according to FIG. 1 in different operating modes.

According to FIG. 1, a device designated as a whole as 14 for carrying out a measuring method for detecting contaminants in a fluid 1 is shown in a schematic diagram. The fluid 1 in the illustrated exemplary embodiment is a rolling oil of a mill train or rolling means which is not detailed and which is correspondingly highly contaminated and has a very high content of metallic, especially ferromagnetic particles, in addition to other contaminants, such as slag.

The device 14 consists essentially of a metering circuit 11 and a primary circuit 12.

The metering circuit 11 has a first metering pump 3 with a stepping motor drive. The first metering pump 3 conveys contaminated fluid 2 with particles. The first valve V₁ is designed as a 3/2 directional control valve and is shown in its enabled position in FIG. 1 in which the contaminated fluid 2, routed via a shavings sensor 15, is routed to a connection 18 of a main hydraulic system, and therefore is supplied in return flow to the indicated mill train. The indicated shavings sensor 15 is optional and is not critically necessary for the actual function of the measuring and dilution means, which is still to be detailed. A third valve V₃ is likewise designed as a 3/2 directional control valve, like the first valve V₁. The third valve V₃, in its operating position shown in FIG. 1, is in a passage position to a fourth valve V₄. The first valve V₁, in its other operating position, furthermore enables the delivery of contaminated fluid 2 to a tank 9, which is part of a mixing means 8, comprising the tank 9 and, in this case, a second valve V₂; said second valve, however, is not critically necessary for the basic function of the device.

The primary circuit 12 essentially comprises the tank 8, an evacuation site 16 for the metering circuit 11, a second metering pump 13, as well as a device 4 for measuring the contamination of the fluid 1, wherein the device 4 can be supplied with a defined mixture of cleaned fluid 5 in the tank 8 and contaminated fluid 2, that is, a type of mixed fluid 6.

The device 4 for measuring the contamination of the fluid 1 can be a so-called contamination sensor CS, as is described, for example, in DE 10 2006 005 956.5. These contamination sensors CS work in the manner of light-based particle sensors, i.e., the particles—after passing through a photoelectric barrier or the like—are determined according to size and number so that the dilution aspect of the measuring fluid, which will be detailed below, acquires increased importance. Only by the indicated dilution or deconcentration of the fluid medium according to the invention within the definable, adjustable framework are the particles to be detected present individually in a statistical distribution in the fluid such that the light-based sensors can respond at all. Without this separation by dilution, only a fluid clouded by the particles could be established without any indication about how the degree of contamination is in fact represented in particular, due to the lack of counting magnitude relative to the general particle contamination. The dilution to be carried out is oriented predominantly to the measuring quality of the respective light sensor to be used.

A pressure control valve 17 located downstream of the device 4 for measuring the contaminants provides for bubble-free, preloaded operation of the device 4. Furthermore, between the second metering pump 13 and the contamination sensor CS, an inlet segment for the fluid, whose length can be defined at will, is represented in the form of a loop. The second valve V₂, which is designed as 2/2 directional control valve, is used as a bypass valve or mixing valve 10 and, in this respect, enables the device 4 and the pressure control valve 17 to be bypassed. In conjunction with the operating position of the third valve V₃ and of the fourth valve V₄, likewise designed as 3/2 directional control valves, which position is shown in FIG. 1, a backflow of mixed fluid 6 into the tank 8 is possible, where, depending on the operating position of the fourth valve V₂, flow through an additional filter 19 can take place or not. However, in the circuit diagram as shown in FIG. 1, in any case, there is flow through the filter 19. The second valve V₂ is not absolutely necessary, and when it is omitted, in each case, there is flow through the contamination sensor CS and the pressure control valve 17.

The first, third, and fourth valves V ₁, V₃, and V₄ are designed as 3/2 directional control valves so that the valve modules used in this respect are designed as identical components; this helps reduce the hardware cost so that the entire device can be economically produced. All valves can preferably be electromagnetically actuated; this, however, is not detailed, for the sake of simplicity.

An arithmetic unit 7, which can be part of a control means and/or regulation means (not detailed), or can be part of the device 4 for measuring the contamination in the fluid, computes the content of particles of contaminants determined by the device 4 back to the actual content of particles of contaminants in the unmixed fluid 2 with the particle contamination from the main hydraulic system which, in this example, transports the rolling oil of the mill train. Instead of the indicated rolling oil, of course any other form of more or less heavily contaminated fluid with ingress of particles can also be treated via the described method and also the device.

FIG. 2 depicts, in the form of a flow chart, one of many operating modes or methods for detecting contaminants with the device 14 shown in FIG. 1. Within the scope of a first operating mode (mode 1), the metering circuit 11 is in a standby mode, and the primary circuit 12 is in a cleaning mode R.

Another operating situation, “cleaning of the oil,” is illustrated in FIG. 3, and in the line part shown with the broken line, preferably a large amount of fluid is moved through the working circuit by means of the stepping motor drive and the metering pump 3 in order to flush, for example, the connected lines; this helps prevent deposits, and fluid with current contamination continues to be supplied via the connection 18 to the main hydraulic system from the input side. Here the valve V₁ is in its illustrated enabled position.

The primary circuit 12 (shown by a bolded line) is supplied with cleaned fluid which is accordingly routed via the filter 19. Here the second valve V₂, and the third and fourth valve V₃, V₄ are in an illustrated operating position such that the fluid flow produced by the second metering pump 13 is routed past the sensor CS or the device 4 by the third valve V₃ and fourth valve V₄ and can be returned in this respect to the tank 9 in a closed circulation. This circulation repeats until a defined degree of purity for the fluid 5 is reached. In this process of cleaning the oil via the filter 19, the stepping motor drive is operating with the second metering pump 13 in the range of large amounts of fluid per unit of time in the primary circuit 12.

In the pure mixing operation for mixing of cleaned fluid 5 with contaminated fluid 2, the valve V₄ is switched such that the filter 19 is then bypassed. Furthermore, it is possible to change into a mode 2 or a mixing mode M by cleaned fluid 5 being mixed in a defined manner with contaminated fluid 2; this largely corresponds to FIG. 4, which shows a “mixing and metering process.” The metering circuit 11 (shown by broken lines) shifts into a prepared supply mode V in which contaminated fluid 2 is supplied to the mixing means 8, here in the form of the tank 9. It has been found for an especially favorable progression of the method that the connecting line between the tank 9 and the valve V ₁ should be dimensioned to be especially short, for example, chosen to have a line length of less than 10 cm. For this charging or admixing process, the metering pump 3 delivers only a small amount of contaminated fluid 2 per unit of time, and, instead of low charging via the pump 3, the valve V₁ can also shift into correspondingly cycled operation in which a certain portion amount from the main line with the rolling oil is always taken into the metering circuit 11 in a stepwise fashion. In this case, the arithmetic unit 7 takes over the cycled operation for the valve V₁.

The third valve V₃ and the fourth valve V₄ are in an illustrated operating position as shown in FIG. 4 in which the filter 19 has passed into this mode so that fluid from the second metering pump 13 in turn is routed to the mixing means 8 at a high flow amount per unit of time.

After a definable waiting or resting time, there is a change to mode 3 in which the metering circuit 11 is in a supply mode Z for contaminated fluid 2 to the mixing means 8, and the primary circuit 12 (in turn shown by the bolded line) remains in a mixing mode M. The operating position of the first valve V ₁ here is such that contaminated fluid 2 is conveyed into the mixing means 8. The operating position of the second valve V₂, and of the third and fourth valve V₃, V₄, as shown in turn in FIG. 4, is such that mixed fluid 6 is moved past the device 4 for measuring the contaminants to the mixing means 8 in the closed circuit.

Depending on the desired purity level, the preferred mixing ratios between contaminated fluid 2 and cleaned fluid 5 are set preferably between 1:10 to approximately 1:150, i.e., for example, that there is one milliliter of contaminated fluid 2 per 10 milliliters of cleaned fluid 5. A definable amount of cleaned fluid 5 has to already be in the tank 9 prior to this admixture process of contaminated fluid via the metering circuit 11. For purposes of explanation, it should be noted that the liquid level in the tank 9 in the figures relates to the minimum liquid level of the tank 9.

After a definable waiting time expires again, the method in the primary circuit 12 (in turn shown by a bolded line) shifts into a so-called measuring mode MM (mode 5). In this measuring operation, which corresponds to the operating representation as shown in FIG. 5, the metering circuit 11 is in an operating mode in which contaminated fluid is routed directly from the input side to the main hydraulic system via the connection 18, comparably to the representation in FIG. 2. How this primary circuit runs is shown in turn by the broken line. The second valve V₂ is in its illustrated blocking position, and the fourth valve V₄ and the third valve V₃ are in their illustrated operating position in which mixed fluid 6 is routed through the device 4 for measuring the contaminant; however, the filter 19 remaining omitted. In turn, per unit of time the metering pump 3 delivers a large amount of fluid, and the metering pump 13 delivers a small amount. The required measurement values are determined individually as soon as their variance does not exceed a certain boundary.

As FIG. 2 furthermore shows, another operating mode (mode 4) is switched between mode 5 and mode 3, in which the metering circuit 11 is shifted into preparation of supply V and the primary circuit 12 into the mixing mode M. In mode 6, the metering circuit 11 is in the standby mode. In a further provided evacuation, a desired liquid level in the tank 9 is attempted, and, in an enabled operating position of the valve V₃, the amount of fluid of the primary circuit 12 is returned as return flow into the main hydraulic system via the connection 18. Then there can again be a change to mode 1 as the operating mode.

In a simplified embodiment (not shown) of the method according to the invention in addition to the device, the tank 9—in addition to the evacuation site 16—can also be omitted, and the valve V₁ on the output side is switched directly to the input side of the second metering pump 13 via the metering circuit 11. In this case, the connecting line between the valve V₁ and the metering pump 13 in turn is chosen to be short, and likewise a short connection between the output of the second metering pump 13 and the input of the contamination sensor CS is aimed for. In the correspondingly simplified embodiment, the bypass valve or mixing valve V₂ can furthermore be omitted, as well as the pressure control valve 17. As already stated, the shavings sensor 15 can also be omitted. The required admixing takes place, as already stated, via connection of the metering pump 3 and preferably by cycled operation of the valve V₁, which can then transfer contaminated fluid 2 in batches into the metering circuit 11.

In a further simplified embodiment which is not shown, the contaminated fluid with the particle contamination, such as, for example, rolling oil, is routed quantitatively controlled directly via the metering pump 3 to the input of the second metering pump 13, which on its output side then has the device 4 for measuring the contaminants, and in a branch upstream of the second metering pump 13 it can convey fresh oil from a supply source, such as, for example, a barrel. This extremely simple solution manages without any valve control and therefore without valves which must be actuated. In turn, the fluid which has been measured in this way via the contamination sensor CS is then returned to the main hydraulic system, for example in the form of the mill train.

Instead of the tank 9 or the indicated branch between the metering pumps 3 and 13, there can also be a mixing valve, which is not defined in detail, and which then in turn undertakes admixing actuated via the arithmetic unit 7. Furthermore, for an embodiment of the measuring and admixing device, which is not detailed, the metering circuit 11, with a supply line coming directly from the valve V₁, can be switched upstream of the contamination sensor CS; this aids integration of the device into all possible valve blocks. The supply line therefore ends downstream of the other metering pump 13 in the fluid segment to the sensor CS. 

1. A method for detecting contaminants in a fluid (1), wherein the particle-contaminated fluid (2) is conveyed with a first metering pump (3) to a device (4) for measuring the contamination or particle density in the contaminated fluid, characterized in that the particle-contaminated fluid (2) before entering the device (4) for measuring the contamination is mixed with a cleaned fluid (5) in a defined mixing ratio, the particle density or the contamination of the mixed fluid (6) is measured, and the particle density or the contamination of the contaminated fluid (2) is determined by an arithmetic unit (7).
 2. The method for detecting contaminants in a fluid (1) according to claim 1, characterized in that the contaminated fluid (2) and the cleaned fluid (5) are mixed with one another in a mixing means (8).
 3. The method for detecting contaminants in a fluid (1) according to claim 2, characterized in that the mixing means (8) is a tank (9) and/or a mixing valve.
 4. A device for carrying out the method according to claim 1, characterized in that there is a metering circuit (11) with which contaminated fluid (2) is conveyed by the first metering pump (3) to the device (4) for measuring the contaminants, and that there is a first valve (V1) downstream of the first metering pump (3), the metering circuit (11), depending on the operating position of the valve (V1), conveying contaminated fluid (2) either into a tank (9) or in the direction of a connection (18) to a main hydraulic system.
 5. The device according to claim 4, characterized in that a primary circuit (12) comprises a second metering pump (13), which conveys contaminated and cleaned fluid (2, 5) to the device (4) for measuring the contamination, a third valve (V3) and a fourth valve (V4) being provided and, depending on the operating position of the valves (V3, V4) of the primary circuit (12), either a cleaning mode (R) or a mixing mode (M) for cleaned and contaminated fluid (5, 2), or a measuring mode (MM), or an evacuation mode for the metering circuit (11) and/or the primary circuit (12) can be operated.
 6. The device according to claim 5, characterized in that there is a combination of the metering circuit (11) and of the primary circuit (12) such that the metering circuit (11) is operated in a standby mode and the primary circuit (12) is operated in a cleaning mode (R).
 7. The device according to claim 6, characterized in that the first metering pump (3) is in operation, the first valve (V1) is in an operating position in which a fluid-carrying connection to the main hydraulic system is established, and the second, third, and fourth valves (V2, V3, V4) have an operating position such that a fluid flow with cleaned fluid (5) travels from the tank (9) via the second metering pump (13) to the second valve (V2) and is routed via the third and fourth valve (V3, V4) to a filter (19) and is again returned to the tank (9).
 8. The device according to claim 5, characterized in that there is a combination of the metering circuit (11) and the primary circuit (12) such that the metering circuit (11) is operated in a preparation mode (V) for supply of the contaminated fluid (2) to the mixing means (8) and the primary circuit (12) is in a mixing mode (M) for contaminated and cleaned fluid (2, 5).
 9. The device according to claim 8, characterized in that the first metering pump (3) is in operation and the first valve (V1) is in an operating position in which contaminated fluid (2) is routed to the tank (9), the second valve (V2) as well as the third valve (V3) and the fourth valve (V4) being in one operating position, that a fluid flow is routed from the second metering pump (13) to the mixing means (8), bypassing the device (4) for measuring the contamination of the fluid (1) and bypassing the filter (19).
 10. The device according to claim 5, characterized in that there is a combination of the metering circuit (11) and the primary circuit (12) such that the metering circuit (11) is in a supply mode (Z) for contaminated fluid (2) and the primary circuit (12) is in a mixing mode (M) for contaminated fluid (2) and cleaned fluid (5).
 11. The device according to claim 10, characterized in that the first metering pump (3) is in operation and the first valve (V1) conveys the contaminated fluid (2) into the mixing means (8) and the operating position of the second valve (V2), of the third valve (V3), and of the fourth valve (V4) is such that the mixed fluid (6) on the device (4) for measuring the contamination is routed past the mixing means (8) again to this mixing means (8).
 12. The device according to claim 5, characterized in that there is a combination of the metering circuit (11) and of the primary circuit (12) such that the metering circuit (11) is in a preparation mode (V) for supply of contaminated fluid (2) and the primary circuit (12) is in measuring mode (MM).
 13. The device according to claim 12, characterized in that the first metering pump (3) is in operation and the first valve (V1) routes the contaminated fluid (2) to the main hydraulic system, the second valve (V2) being in a blocking position so that mixed fluid (6) is routed through the device (4) for measuring the contamination and the third valve (V3) and the fourth valve (V4) are in one operating position, and that measured fluid is returned to the tank (9).
 14. The device according to claim 5, characterized in that there is a combination of the metering circuit (11) and of the primary circuit (12) such that the contaminated fluid (2) in the metering circuit (11) is not moved and the cleaned and/or mixed fluid (5, 6) can be evacuated from the mixing means (8) into the primary circuit (12).
 15. The device according to claim 14, characterized in that the second valve (V2) assumes an operating position such that contaminated fluid (2) is routed to the third valve (V3), and from the third valve (V3) the fluid (2) is routed to the main hydraulic system via the connection (18), the fourth valve (V4) assuming a blocking operating position, which valve enables an evacuation of the metering circuit (11) and of the main circuit (12), the valve (V1) passing contaminated fluid likewise into the connection (18) of the main hydraulic system.
 16. The device according to claim 4, characterized in that the device (14) has a sensor element (CS) such as, for example, an optical or Hall sensor, which determines the quantity of contamination particles and transmits it to a control means and/or regulation means which controls the metering circuit (11) and the main circuit (12) by means of the valves (V1, V2, V3, V4) and the metering pumps (3, 13).
 17. The device according to claim 7, characterized in that the device (14) has a collecting site for collecting contaminants and at the collecting site has a permanent magnet for generating a magnetic field and a coil, wherein by energizing the coil, an element of the device (14) is able to be moved and, by moving the element, the magnetic field strength at the collecting site is able to be changed. 